TedEd-30

Could a Breathalyzer
Detect Cancer?

How is it that a breathalyzer can measure the alcohol content in someone’s blood, hours after they
had their last drink, based on their breath alone? Exhaled breath contains trace amounts ofhundreds, even thousands, of volatile organic compounds: small molecules lightweight enough totravel easily as gases. One of these is ethanol, which we consume in alcoholic drinks. It travels
through the bloodstream to tiny air sacs in the lungs, passing into exhaled air at a concentration
2,000 times lower, on average, than in the blood. When someone breathes into a breathalyzer, theethanol in their breath passes into a reaction chamber. There, it’s converted to another molecule,called acetic acid, in a special type of reactor that produces an electric current during the reaction.
The strength of the current indicates the amount of ethanol in the sample of air, and by extension in
the blood. In addition to the volatile organic compounds like ethanol we consume in food and drink,the biochemical processes of our cells produce many others. And when something disrupts thoseTedEd-30

Could a Breathalyzer
Detect Cancer?

processes, like a disease, the collection of volatile organic compounds in the breath may change,too.
So could we detect disease by analyzing a person’s breath, without using more invasive diagnostic
tools like biopsies, blood draws, and radiation? In theory, yes, but testing for disease is a lot more
complicated than testing for alcohol. To identify diseases, researchers need to look at a set of tensof compounds in the breath. A given disease may cause some of these compounds to increase ordecrease in concentration, while others may not change — the profile is likely to be different forevery disease, and could even vary for different stages of the same disease. For example, cancers
are among the most researched candidates for diagnosis through breath analysis. One of thebiochemical changes many tumors cause is a large increase in an energy-generating process called
glycolysis. Known as the Warburg Effect, this increase in glycolysis results in an increase of
metabolites like lactate which in turn can affect a whole cascade of metabolic processes andultimately result in altered breath composition, possibly including an increased concentration ofvolatile compounds such as dimethyl sulfide. But the Warburg Effect is just one potential indicator ofcancerous activity, and doesn’t reveal anything about the particular type of cancer. Many moreindicators are needed to make a diagnosis.
To find these subtle differences, researchers compare the breath of healthy people with the breathof people who suffer from a particular disease using profiles based on hundreds of breath samples.
This complex analysis requires a fundamentally different, more versatile type of sensor from thealcohol breathalyzer. There are a few being developed. Some discriminate between individualcompounds by observing how the compounds move through a set of electric fields. Others use anarray of resistors made of different materials that each change their resistance when exposed to acertain mix of volatile organic compounds. There are other challenges too. These substances arepresent at incredibly low concentrations — typically just parts per billion, much lower than ethanol

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Could a Breathalyzer
Detect Cancer?

concentrations in the breath. Compounds’ levels may be affected by factors other thandisease,including age, gender, nutrition, and lifestyle. Finally, there’s the issue of distinguishing
which compounds in the sample were produced in the patient’s body and which were inhaled fromthe environment shortly before the test. Because of these challenges, breath analysis isn’t quite
ready yet. But preliminary clinical trials on lung, colon, and other cancers have had encouraging
results. One day, catching cancer early might be as easy as breathing in and out.